Suspension apparatus

ABSTRACT

A suspension apparatus includes: a partition wall member that divides a space inside an inner tube into an upper space and a lower space; a cap that covers an upper opening portion of an outer tube; and a support member of which one end portion is retained by the cap, and of which the other end portion supports the other end portion of a piston rod, in which a through-hole is formed in a portion of the inner tube, an inner space of the piton rod is a space inside the piston rod and communicates with the lower space, the support member is a cylindrical member and forms an upper portion space, and the upper portion space communicates with the inner space of the piston rod, and at least one of the cap and the support member is provided with a communication path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. 119from Japanese Patent Application No. 2013-209723 filed on Oct. 4, 2013,the entire content of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a suspension apparatus that is arrangedbetween a vehicle body and a wheel in a two-wheeled vehicle or the like.

2. Related Art

In the related art, in a front fork in a two-wheeled vehicle known as anexample of a suspension apparatus, bushes are fixed to an upper portionand a lower portion of an inner circumference of an outer tube, an innertube is slidably fitted into the outer tube via the upper and the lowerbushes, an annular oil chamber that is defined by the upper and thelower bushes is formed in a space between the inner circumference of theouter tube and an outer circumference of the inner tube, and thus avolume compensation chamber is formed to compensate for a volumeaffected by entry and retreat of a piston rod during a stroke of apiston.

In this type of the suspension apparatus, a hydraulic shock absorberaccording to JP-A-2009-85263 has a partition wall member which ismounted to the inside on an opening end side of the inner tube so thatthe partition wall chamber guides the piston rod mounted to the outertube. The partition wall member is configured to have a cylindricalportion that is formed into a cylindrical shape along an innercircumference of the inner tube, and a bottom portion that is providedto block the bottom of the cylindrical portion. In a state where thecylindrical portion is screwed into the inner tube and the bottomportion is positioned inside the inner tube, using the bottom portion asa reference portion, the partition wall member divides a working oilchamber that is formed below the bottom portion from an oil reservoirchamber which is formed above the bottom portion. A piston mounted tothe piston rod that is fixed to the outer tube slides inside the workingoil chamber. The oil reservoir chamber supplies working oil to theworking oil chamber and vice versa. The working oil chamber communicateswith the annular oil chamber through an oil hole provided in the innertube, and the working oil freely circulates therebetween. When thehydraulic shock absorber is compressed, the working oil flows from theworking oil chamber into the annular oil chamber by a volume taken up bythe piston rod entering the working oil chamber by a stroke. When thehydraulic shock absorber is extended, the working oil flows from theannular oil chamber into the working oil chamber by a volume freed up bythe piston rod retreating from the working oil chamber by a stroke.Accordingly, a volume affected by entry and retreat of the piston rod iscompensated for, and a predetermined damping force is obtained. Inaddition, in the hydraulic shock absorber according to JP-A-2009-85263,a plurality of adjusting portions are provided in a cap that seals anupper end opening portion of the outer tube, and the plurality ofadjusting portions are placed side by side in a plan view of the cap.Each of the plurality of adjusting portions is configured to have anadjusting bolt and the adjusting portions have a plurality of adjustingnuts that match with the respective adjusting bolts. Each of theadjusting nuts has a screwed hole into which one adjusting bolt matchingwith one adjusting nut is screwed, and another hole that is a guide holeinto which another adjusting bolt is inserted. When one of the adjustingbolts is rotated, one of the adjusting nuts into which the adjustingbolt is screwed is configured in such a manner that the adjusting nut isnot rotated and is guided to move axially due to engagement of the guidehole of the adjusting nut and the other adjusting bolt.

SUMMARY OF INVENTION

In the suspension apparatus according to JP-A-2009-85263, there is aproblem in that air bubbles in working oil gradually gather around theplurality of adjusting bolts that are provided in each of the pluralityof adjusting portions and air bubble entrapment is formed. Duringextension operation in a case where the air bubble entrapment is formedin these portions, since a predetermined damping force is obtained afterthe air bubble entrapment is compressed by the working oil, dampingoperation is delayed. In addition, since the supply of the working oilinto an oil chamber formed below the piston inside the working oilchamber is delayed, pressure in the oil chamber rapidly decreases, agaseous component in the working oil is separated, and an air bubblegrows. Thereafter, during compression operation, an impulse sound occursat the time a growing air bubble is instantaneously compressed todissipate.

An object of the invention is to provide a suspension apparatus that cansuppress occurrence of an impulse sound caused by occurrence of airbubble entrapment in a space in which air is present and in whichpressure increases during extension operation.

[1] According to an aspect of the invention, it provides that ansuspension apparatus includes a cylindrical outer tube; an inner tubewhich is coaxially arranged inside the outer tube to move in an axialdirection relative to the outer tube; a piston inserted into the innertube; a piston rod of which one end portion retains the piston and whichmoves together with the outer tube with respect to the inner tube; apartition wall member that is mounted to an upper end portion of theinner tube to define an upper end portion of an annular oil chamberwhich is formed between an inner circumferential surface of the outertube and an outer circumferential surface of the inner tube, that has abowl portion formed into a bowl shape located inside the inner tube, andthat divides a space inside the inner tube into an upper space which isa space above the bowl portion and a lower space which is a space belowthe bowl portion; a cap that covers an upper opening portion of theouter tube; a support member of which one end portion is retained by thecap, and of which the other end portion supports the other end portionof the piston rod. A through-hole is formed in a portion of the innertube which is below the partition wall member to communicate the annularoil chamber with the lower space. An inner space of the piston rod is aspace inside the piston rod and communicates with the lower space. Thesupport member is a cylindrical member and forms an upper portion spacebetween the cap and the support member, and the upper portion spacecommunicates with the inner space of the piston rod. At least one of thecap and the support member is provided with a communication path throughwhich the upper portion space communicates with the upper space.

[2] The suspension apparatus may provide that the cap has an abuttingsurface against which an upper end surface of the support member abuts.The communication path has an upward concave portion that is concaveupward from the abutting surface of the cap. The suspension apparatusfurther includes a non-return valve that is arranged between theabutting surface of the cap and the upper end surface of the supportmember. The non-return valve allows flow of air from the upper portionspace to the upper space through the communication path, and suppressesflow of air from the upper space to the upper portion space.

[3] The suspension apparatus may provide that the communication path isa communication hole that is formed in a portion of the support memberwhich is below the cap, and the upper portion space communicates withthe upper space through the communication path. Rubber is arrangedaround the support member in the upper space.

[4] The suspension apparatus may provide that the piston retains adividing member that divides the lower space into an upper positioningspace which is a space positioned above the dividing member and a lowerpositioning space which is a space positioned below the dividing member,and the piston has a space communication hole that is a hole tocommunicate the upper positioning space with the lower positioningspace. The suspension apparatus further includes an adjustment mechanismthat adjusts the rate of a fluid passing through the space communicationhole of the piston. An operation portion operating the adjustmentmechanism is arranged inside the upper portion space.

With the configuration of [1], the through-hole is formed in a portionof the inner tube which is below the partition wall member in order forthe annular oil chamber to communicate with the lower space. The innerspace of the piston rod is a space inside the piston rod andcommunicates with the lower space. The support member is a cylindricalmember and forms the upper portion space between the cap and the supportmember, and the upper portion space communicates with the inner space ofthe piston rod. At least one of the cap and the support member isprovided with the communication path through which the upper portionspace communicates with the upper space. For this reason, it is possibleto suppress occurrence of an impulse sound caused by occurrence of airbubble entrapment in a space in which air is present and in whichpressure increases during extension operation.

With the configuration of [2], the cap has the abutting surface againstwhich the upper end surface of the support member abuts. Thecommunication path is configured to contain the upward concave portionthat is concave upward from the abutting surface of the cap. Thenon-return valve that is arranged between the abutting surface of thecap and the upper end surface of the support member, allows flow of airfrom the upper portion space to the upper space through thecommunication path, and suppresses flow of air from the upper space tothe upper portion space. Accordingly, during extension operation, it ispossible to discharge air bubbles from a space in which air is presentand in which pressure increases during extension operation, and duringcompression operation, it is possible to suppress suction of air intothe space.

With the configuration of [3], the communication path is a communicationhole that is formed in the portion of the support member which is belowthe cap, and the upper portion space communicates with the upper spacethrough the communication path. The rubber is arranged around thesupport member in the upper space. Accordingly, during extensionoperation, it is possible to discharge air bubbles from the space inwhich air is present and in which pressure increases during extensionoperation, and during compression operation, it is possible to suppressthe suction of air into the space.

With the configuration of [4], the piston retains the dividing memberthat divides the lower space into the upper positioning space which is aspace positioned above the dividing member and the lower positioningspace which is a space positioned below the dividing member, and thepiston has the space communication hole that is a hole through which theupper positioning space communicates with the lower positioning space,and thus, even in a configuration where the suspension apparatus furtherincludes the adjustment mechanism that adjusts the rate of a fluidpassing through the space communication hole of the piston, and theoperation portion for operation of the adjustment mechanism is arrangedinside the upper portion space, it is possible to suppress occurrence ofthe impulse sound caused by occurrence of the air bubble entrapment inthe space in which the operation portion is arranged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a motorcycleaccording to an embodiment.

FIG. 2 is a cross-sectional view of a front fork according to theembodiment of the invention.

FIG. 3 is an enlarged view of a portion III in FIG. 2.

FIG. 4 is an enlarged view of a portion IV in FIG. 2.

FIG. 5 is a perspective view when a rod guide case is seen from below.

FIG. 6 is a view illustrating a schematic configuration of a firstoperation portion and a second operation portion.

FIGS. 7A and 7B are views illustrating operation of an extension stroke.

FIGS. 8A and 8B are views illustrating operation of a compressionstroke.

FIG. 9A is a view illustrating cross-sections of a cap, a supportmember, a stopper rubber and an outer tube.

FIG. 9B is a cross-sectional view of a portion IX-IX in FIG. 9A.

FIG. 10 is a view illustrating cross-sections of the cap, the supportmember, the stopper rubber and the outer tube according to anotherembodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detailwith reference to the accompanying drawings.

FIG. 1 is a view illustrating a schematic configuration of a motorcycle1 according to the embodiment.

The motorcycle 1 includes a front wheel 2 that is a wheel on a frontside; a rear wheel 3 that is a wheel on a rear side; and a main vehiclebody 10 having a vehicle frame 11 that is a skeleton of the motorcycle1, a handlebar 12, an engine 13 and the like. In addition, a front fork21 is an example of a suspension apparatus that connects the front wheel2 to the main vehicle body 10. The motorcycle 1 has a front fork 21 oneach of the left and the right sides of the front wheel 2. Themotorcycle 1 has a rear suspension 22 on each of the left and the rightsides of the rear wheel 3, and the rear suspensions 22 connect the rearwheel 3 to the main vehicle body 10. FIG. 1 illustrates only the frontfork 21 and the rear suspension 22 that are arranged on the right side.In addition, the motorcycle 1 includes two brackets 14 that retain thefront forks 21 arranged on both of the left and the right sides of thefront wheel 2, and a shaft 15 that is arranged between two brackets 14.The shaft 15 is rotatably supported by the vehicle frame 11.

Subsequently, the front fork 21 will be described in detail.

FIG. 2 is a cross-sectional view of the front fork 21 according to theembodiment of the invention.

FIG. 3 is an enlarged view of a portion III in FIG. 2.

FIG. 4 is an enlarged view of a portion IV in FIG. 2.

FIG. 5 is a perspective view when a rod guide case 130 to be describedlater is seen from below.

The front fork 21 according to the embodiment is arranged between themain vehicle body 10 and front wheel 2 of the motorcycle 1 to supportthe front wheel 2, and the front fork 21 is a so-called inverted frontfork in which an inner tube 110 and an outer tube 210 to be describedlater are arranged on a side of the front wheel 2 and a side of the mainvehicle body 10, respectively.

The front fork 21 includes an axle side unit 100 that has the inner tube110 and is mounted to an axle of the front wheel 2; and a main body sideunit 200 that has the outer tube 210 and is mounted to the main vehiclebody 10. In addition, the front fork 21 includes a coil spring 400 thatis arranged between the axle side unit 100 and the main body side unit200 and absorbs vibration exerted on the front wheel 2 due to roadsurface roughness; and a spring support member 410 that supports thecoil spring 400 together with a lower spring receiver 124 to bedescribed later.

The inner tube 110 and the outer tube 210 are substantially cylindricalmembers that are arranged coaxially with each other, and there is a casewhere a direction of the center line (axial direction) of the cylinderis referred to as a “vertical direction” and the side of the mainvehicle body 10 and the side of the front wheel 2 are referred to as anupper side and a lower side, respectively. The axle side unit 100 andthe main body side unit 200 move in the vertical direction (axialdirection) relatively with each other, and thus the front fork 21absorbs road surface roughness to suppress vibration while the frontfork 21 supports the front wheel 2.

Configuration of Axle Side Unit 100

The axle side unit 100 includes the substantially cylindrical inner tube110 of which both ends are open; an axle bracket 120 that is mounted toan end portion (lower end portion) on a lower side of the inner tube 110and the front wheel 2; and an oil seal 125 that seals a gap between theinner tube 110 and the axle bracket 120. In addition, the axle side unit100 includes the rod guide case 130 that is mounted to an end portion(upper end portion) on an upper side of the inner tube 110 to guidemovement of a piston rod 235 of the main body side unit 200 to bedescribed later; an oil ring 135 that seals a gap between the rod guidecase 130 and the outer tube 210; and a supply and discharge apparatus150 that adjusts the circulation of oil between the inside and outsideof the rod guide case 130.

Configuration of Inner Tube 110

The inner tube 110 is formed to have the outer diameter smaller than theinner diameter of the outer tube 210, and in a state where the innertube 110 enters the outer tube 210, an annular oil chamber 20 is formedbetween an outer circumferential surface of the inner tube 110 and aninner circumferential surface of the outer tube 210.

The inner tube 110 has an inner diameter uniformly formed in an innercircumferential surface thereof along the vertical direction so that apiston 220 of the main body side unit 200 to be described later smoothlyslides. Besides, a female screw 111 is formed in the innercircumferential surface of the upper end portion, and a male screw 131 aof the rod guide case 130 to be described later is tightened into thefemale screw 111. Meanwhile, the inner tube 110 has an outer diameteruniformly formed in the outer circumferential surface thereof basicallyalong the vertical direction, and a concave portion 112 is formed overthe entire circumference of the upper end portion. In addition, theinner tube 110 has a male screw 113 formed in an outer circumferentialsurface of the lower end portion, and the male screw 113 is tightenedinto the female screw 121 a of the axle bracket 120 to be describedlater. In addition, a communication hole 114 is formed in a portion ofthe inner tube 110 which is below the rod guide case 130 in a statewhere the rod guide case 130 is mounted to the inner tube 110, and theinside of the inner tube 110 communicates with the annular oil chamber20 through the communication hole 114.

A slide bush 115 is fitted to the aforementioned concave portion 112 sothat the inner tube 110 smoothly slides on the inner circumferentialsurface of the outer tube 210. The slide bush 115 is a bearing that isformed into a cylindrical shape, and in a state where the slide bush 115is mounted on the inner tube 110, the slide bush 115 is set to have anouter diameter larger than that of the inner tube 110 in such a mannerthat an outer circumferential surface of the slide bush 115 protrudesoutward from the outer circumferential surface of the inner tube 110.

A predetermined amount of oil is poured into the inner tube 110.

Configuration of Axle Bracket 120

As illustrated in FIG. 2, the axle bracket 120 has a concave portion 121into which the inner tube 110 is inserted; and an axle mounting hole 122into which the axle of the front wheel 2 can be mounted. The concaveportion 121 of the axle bracket 120 has the female screw 121 a intowhich the male screw 113 is tightened; and a seal groove 121 b in whichthe oil seal 125 is fitted to seal a gap between the outercircumferential surface of the inner tube 110 and the concave portion121. In addition, the lower spring receiver 124 is mounted in theconcave portion 121, and a lower end portion of the coil spring 400 isplaced on the lower spring receiver 124 that receives a spring load.

When the male screw 113 of the inner tube 110 is tightened into thefemale screw 121 a, the axle bracket 120 is mounted to block an openingof the lower end portion of the inner tube 110. The oil seal 125 fittedinto the seal groove 121 b of the concave portion 121 seals the gapbetween the outer circumferential surface of the inner tube 110 and theaxle bracket 120, and thus oil poured into the inner tube 110 isprevented from leaking.

Configuration of Rod Guide Case 130

As illustrated in FIGS. 3 and 5, the rod guide case 130 includes acylindrical portion 131 which is formed in such a manner that adirection of the center line thereof is the vertical direction; aninward portion 132 that is provided below an lower end portion of thecylindrical portion 131 and is formed to face inward in a radialdirection so that the inward portion 132 blocks an opening of the lowerend portion; and an outward portion 133 that is formed to face outwardin the radial direction above an upper end portion of the cylindricalportion 131.

The male screw 131 a is formed in an outer circumferential surface ofthe upper end portion of the cylindrical portion 131, and the male screw131 a is tightened into the female screw 111 formed in the inner tube110. In a portion below the male screw 131 a, the cylindrical portion131 is formed to have an outer diameter smaller than the inner diameterof the inner tube 110, and in a state where the rod guide case 130 ismounted to the inner tube 110, an annular gap 25 (refer to FIGS. 7A and7B as well) is formed between an outer circumferential surface of thecylindrical portion 131 and the inner circumferential surface of theinner tube 110. In addition, a communication hole 131 c is formed in thelower end portion of the cylindrical portion 131 in order for the insideof the cylindrical portion 131 to communicate with the outside thereof.In addition, a cylindrical portion side concave portion 131 d that isconcave inward is formed in an outer circumferential surface of theupper end portion of the cylindrical portion 131, and the cylindricalportion side concave portion 131 d is formed in the vertical directionfrom the top of the male screw 131 a to the bottom thereof and in acircumferential direction at a position corresponding to a position ofan outward portion side concave portion 133 c to be described later.

The inward portion 132 has a valve chamber 140 formed in a centerportion using a through-hole that passes through the inward portion 132in the vertical direction. The supply and discharge apparatus 150 isarranged in the valve chamber 140. In addition, a seal groove 132 b isformed in an outer circumferential surface of the inward portion 132,and an oil seal 145 is fitted to the seal groove 132 b to seal a gapbetween the outer circumferential surface of the inward portion 132 andthe inner circumferential surface of the inner tube 110.

The valve chamber 140 is configured to have a through-hole 132 a thatpasses through the inward portion 132; and a first concave portion 141and a second concave portion 142 that are concave from a lower endsurface of the inward portion 132. The first concave portion 141 and thesecond concave portion 142 are different columnar concavities from eachother in such a manner that a diameter decreases from the lower endsurface to an upper end surface, and the first concave portion 141 is acolumnar concave portion of a large diameter and the second concaveportion 142 is a columnar concave portion of a small diameter. Inaddition, a groove 141 a is formed over the entire circumference of aninner circumferential surface of the first concave portion 141, and thegroove 141 a is concave outward from the inner circumferential surface.

A ring groove 133 a is formed over the circumferential entirety of anouter circumferential surface of the outward portion 133, and the oilring 135 is fitted to the ring groove 133 a to seal a gap between theinner circumferential surface of the outer tube 210 and the rod guidecase 130. The oil ring 135 inserted into the ring groove 133 a functionsas a member that defines an upper portion of the aforementioned annularoil chamber 20.

A lower end surface 133 b of the outward portion 133 functions as anabutting surface against which an upper end surface of the inner tube110 abuts. That is, the lower end surface 133 b of the outward portion133 is formed in a surface orthogonal to the vertical direction, and thelower end surface 133 b is in contact with the entire circumference ofthe upper end surface of the inner tube 110 and tightly seals an innerspace of the inner tube 110. The outward portion side concave portion133 c that is concave upward from the lower end surface 133 b is formedas a partial circumferential area in the outward portion 133 at aposition corresponding to a position of the cylindrical portion sideconcave portion 131 d in the cylindrical portion 131. In other words, asillustrated in FIGS. 3 and 5, the outward portion side concave portion133 c and the cylindrical portion side concave portion 131 d arecontinuously formed and function as a communication path 40 that is acommunication path through which the annular oil chamber 20 communicateswith the annular gap 25.

In the rod guide case 130 having the aforementioned configuration, theinward portion 132 divides a space in the inner tube 110 into a spaceabove the inward portion 132 and a space below the inward portion 132.In addition, the cylindrical portion 131 divides the space above theinward portion 132 into a space inside the cylindrical portion 131 and aspace outside the cylindrical portion 131. A portion above the inwardportion 132 and inside the cylindrical portion 131 functions as an oilreservoir chamber 45 in which oil is stored. In addition, the spacebelow the inward portion 132 and inside the inner tube 110 functions asa working oil chamber 50 in which oil is stored to generate main dampingforce. In addition, a portion above the inward portion 132 and outsidethe cylindrical portion 131 is the aforementioned annular gap 25. Theoil seal 145 which is fitted to the seal groove 132 b formed in theinward portion 132 divides the annular gap 25 from the working oilchamber 50.

In other words, the rod guide case 130 retaining the oil ring 135 andthe oil seal 145 is mounted to the upper end portion of the inner tube110 to define an upper end portion of the annular oil chamber 20 that isformed between the inner circumferential surface of the outer tube 210and the outer circumferential surface of the inner tube 110. The rodguide case 130 has, as an example of a bowl portion that is formed intoa bowl shape, the cylindrical portion 131 and the inward portion 132inside the inner tube 110, and the rod guide case 130 functions as apartition wall member that divides the space inside the inner tube 110into the oil reservoir chamber 45 as an example of an upper space of thecylindrical portion 131 and the inward portion 132 and the working oilchamber 50 and the annular gap 25 as examples of a lower space. The rodguide case 130 retaining the oil ring 135 and the oil seal 145 dividesthe working oil chamber 50 and the annular gap 25 as the examples of thelower space into the annular gap 25 as an example of a gap space betweenthe rod guide case 130 and the inner tube 110 and the working oilchamber 50 as an example of a space other than the annular gap 25. Inthe rod guide case 130, the communication hole 131 c is formed in orderfor the oil-containing oil reservoir chamber 45 to communicate with theannular gap 25, and the communication path 40 is provided in order foran upper portion of the annular oil chamber 20 to communicate with theannular gap 25.

An upper space of the oil reservoir chamber 45 inside the inner tube 110is connected to an upper space inside the outer tube 210, and both ofthe spaces are filled with air. A lower portion of the oil reservoirchamber 45 functions as an oil chamber 46 in which oil poured into theinner tube 110 is stored, and the upper space of the oil reservoirchamber 45 and the upper space inside the outer tube 210 function as anair chamber 47.

Configuration of Supply and Discharge Apparatus 150

As illustrated in FIG. 3, the supply and discharge apparatus 150includes a check valve 151 that allows the flow of oil from the oilreservoir chamber 45 to the working oil chamber 50 and prevents the flowof oil from the working oil chamber 50 to the oil reservoir chamber 45;a backup spring 152 that is arranged below the check valve 151; a springseat 153 which is arranged below the backup spring 152 and on which thebackup spring 152 is seated; and a stopper ring 154 that prevents thecheck valve 151, the backup spring 152 and the spring seat 153 fromfalling off.

The check valve 151 is a cylindrical member, and a flange 151 a isformed in a lower end portion of the check valve 151. A cylindrical bush151 b is press-fitted into an inner circumference of the check valve 151to slidably support the piston rod 235. The flange 151 a is arranged inthe second concave portion 142 of the valve chamber 140, and the checkvalve 151 moves in the vertical direction along an outer circumferenceof the piston rod 235 in such a manner that an upper end surface of theflange 151 a is in contact with a bottom portion (upper end surface) ofthe second concave portion 142, or the upper end surface of the flange151 a is apart from the bottom portion of the second concave portion142.

For example, the backup spring 152 is a disc spring-like member, and ina state where the backup spring 152 is seated on the spring seat 153,the backup spring 152 is in contact with a lower end surface of theflange 151 a of the check valve 151 at a plurality of circumferentiallocations in an inner circumferential or outer circumferential portionthereof.

The spring seat 153 is a disc-shaped member and a hole is formed in acenter portion thereof. Concave and convex portions are alternatelyformed in a circumferential direction, and the concave and convexportions are concave and convex in a radial direction in an outercircumferential portion of the spring seat 153. The spring seat 153 isarranged in the first concave portion 141 of the valve chamber 140 andoil circulates through the concave portions formed on the outercircumferential portion.

The stopper ring 154 is a C-shaped retaining ring and is fitted into thegroove 141 a formed in an inner circumferential surface of the firstconcave portion 141 of the valve chamber 140. The stopper ring 154 isarranged below the spring seat 153 to support the spring seat 153 frombelow.

Configuration of Main Body Side Unit 200

As illustrated in FIG. 2, the main body side unit 200 includes asubstantially cylindrical outer tube 210 of which both ends are open; aguide bush 211 that is mounted to a side of a lower end portion (lowerend portion) of the outer tube 210; an oil seal 212 that is mountedbelow the guide bush 211; and a dust seal 213 that is mounted below theoil seal 212.

In addition, the main body side unit 200 includes the piston 220 thatslides in the working oil chamber 50 formed in the inner space of theinner tube 110; a piston bolt 230 that retains the piston 220; and thepiston rod 235 that retains the piston bolt 230 in a lower end portionthereof.

In addition, the main body side unit 200 includes a cap 240 that ismounted to a side of an upper end portion (upper end portion) of theouter tube 210 to block an upper opening portion; a support member 250that is mounted to the cap 240 to support an upper end portion of thepiston rod 235. In addition, the main body side unit 200 includes acylindrical stopper rubber 255 that is arranged in an annular concaveportion formed by an inner circumference of a cylindrical portion 241 ofthe cap 240 to be described later and an outer circumference of a firstcylindrical portion 251 of the support member 250; a disc-shaped stopperplate 256 that is arranged below the stopper rubber 255; and a stopperring 257 that is arranged below the stopper plate 256.

In addition, the main body side unit 200 includes a damping forcegenerating apparatus 260 that generates a damping force using viscousresistance of oil; and a clamping force adjusting apparatus 270 thatadjusts a damping force of the damping force generating apparatus 260.In addition, the main body side unit 200 includes the spring supportmember 410 that supports the coil spring 400 together with the lowerspring receiver 124.

Configuration of Outer Tube 210

As illustrated in FIG. 2, the outer tube 210 is a substantiallycylindrical member. The lower end portion of the outer tube 210 isexpanded in diameter in such a manner that the guide bush 211, the oilseal 212 and the dust seal 213 can be retained thereinside. A femalescrew 210 a is formed in an inner circumferential surface of the upperend portion thereof, and a male screw 241 a formed in the cap 240 istightened into the female screw 210 a.

The guide bush 211 is a member that helps smooth sliding between theinner circumferential surface of the outer tube 210 and an outercircumferential surface of the inner tube 110. The guide bush 211 is abearing that is formed into a cylindrical shape. In a state where theguide bush 211 is mounted to the outer tube 210, the guide bush 211 isset to have an inner diameter smaller than that of outer tube 210 insuch a manner that an inner circumferential surface of the guide bush211 protrudes inward from the inner circumferential surface of the outertube 210. The guide bush 211 functions as a member that defines a lowerportion of the aforementioned annular oil chamber 20.

The oil seal 212 prevents the working oil which leaks out of the guidebush 211 during mutual sliding of the outer tube 210 and the inner tube110 from flowing to the outside.

The dust seal 213 suppresses intrusion of foreign substances such aswater or dust into the front fork 21 from the outside.

Configuration of Piston 220

As illustrated in FIG. 4, the piston 220 is a cylindrical member thathas a plurality of oil paths formed in the vertical direction. Morespecifically, the piston 220 has a bolt hole 220 a which passes in thevertical direction through a center portion thereof and through which athird cylindrical portion 233 of the piston bolt 230 to be describedlater passes; a first oil path 220 b that is configured by a hole whichpasses in the vertical direction through a portion farther radiallyoutside than the bolt hole 220 a; and a second oil path 220 c that isconfigured by a hole which passes in the vertical direction through aportion farther radially outside than the first oil path 220 b. Inaddition, a ring groove 220 d is formed over the circumferentialentirety of an outer circumferential surface of the piston 220, and anoil ring 221 is fitted to the ring groove 220 d to seal a gap betweenthe outer circumferential surface of the piston 220 and the innercircumferential surface of the inner tube 110. The oil ring 221 fittedto the ring groove 220 d divides the working oil chamber 50 into apiston rod side oil chamber 51 as an example of the upper positioningspace that is an oil chamber which is positioned above the oil ring 221and in which the piston rod 235 is present; and a piston side oilchamber 52 that is an oil chamber as an example of the lower positioningspace which is positioned below the oil ring 221. That is, the piston220 retaining the oil ring 221 divides the working oil chamber 50 intothe piston rod side oil chamber 51 and the piston side oil chamber 52.The aforementioned first oil path 220 b and the second oil path 220 cfunction as communication paths through which the piston rod side oilchamber 51 communicates with the piston side oil chamber 52. The piston220 configures a part of the damping force generating apparatus 260. Thedamping force generating apparatus 260 will be in detail describedlater.

Configuration of Piston Bolt 230

As illustrated in FIG. 4, the piston bolt 230 has a first cylindricalportion 231 that has a cylindrical shape; a second cylindrical portion232 that has a cylindrical shape and is formed to extend downward from alower end portion of the first cylindrical portion 231; and the thirdcylindrical portion 233 that has a cylindrical shape and is formed toextend downward from a lower end portion of the second cylindricalportion 232. A female screw 231 a is formed in an inner circumferentialsurface of the first cylindrical portion 231, and a male screw 235 b tobe described later formed in the piston rod 235 is tightened into thefemale screw 231 a. In addition, a male screw 233 a is formed in a lowerend portion of the third cylindrical portion 233. In addition, athrough-hole 232 a is formed in the second cylindrical portion 232 in aradial direction (a direction orthogonal to the vertical direction) inorder for the inside of the second cylindrical portion 232 tocommunicate with the outside thereof. The through-hole 232 a and aninner portion of the third cylindrical portion 233 function as a bypass60 that bypasses the first oil path 220 b and second oil path 220 cformed in the piston 220 in order for the piston rod side oil chamber 51to communicate with the piston side oil chamber 52.

Configuration of Piston Rod 235

The piston rod 235 is a cylindrical member. As illustrated in FIG. 3, amale screw 235 a is formed in an outer circumferential surface of theupper end portion, and the male screw 235 a is tightened into a femalescrew 252 a to be described later formed in the support member 250. Asillustrated in FIG. 4, the male screw 235 b is formed in an outercircumferential surface of a lower end portion of the piston rod 235,and the male screw 235 b is tightened into the female screw 231 a formedin the piston bolt 230. In addition, in the piston rod 235, athrough-hole 235 c is formed in a radial direction in a portion abovethe male screw 235 b in order for the inside of the piston rod 235 tocommunicate with the outside thereof. When the through-hole 235 c isseen in a direction orthogonal to the vertical direction, thethrough-hole 235 c is formed into an oblong hole shape that is long inthe vertical direction. In addition, the through-holes 235 c are formedat 180 degree intervals circumferentially in an outer circumferentialsurface of the piston rod 235.

When the piston rod 235 has an outer diameter Do in the outercircumferential surface, an area of πDo²/4 is referred to as “across-sectional area of the piston rod 235” hereinafter. Thecross-sectional area of the piston rod 235 according to the embodimentis set to be smaller than a cross-sectional area (an area of across-section cut by a surface orthogonal to the vertical direction) ofthe annular oil chamber 20.

Configuration of Cap 240

As illustrated in FIG. 3, the cap 240 has the cylindrical portion 241that has a cylindrical shape; an inward portion 242 that is provided inan upper end portion of the cylindrical portion 241 and is formed inwardin a radial direction to block an opening; and a columnar portion 243that has a columnar shape and protrudes downward from a lower endsurface of a center portion of the inward portion 242.

The male screw 241 a and a seal groove 241 b are formed in an outercircumferential surface of the cylindrical portion 241. The male screw241 a is tightened into the female screw 210 a formed in the innercircumferential surface of the outer tube 210, and a seal member 245 isfitted to the seal groove 241 b to seal a gap between the outercircumferential surface of the cylindrical portion 241 and the innercircumferential surface of the outer tube 210 in a portion above themale screw 241 a. In addition, a protrusion portion 241 c is providedabove the seal groove 241 b in the outer circumferential surface of thecylindrical portion 241, and the protrusion portion 241 c protrudes in aradial direction outward from the outer circumferential surface of thecylindrical portion 241.

A male screw 243 a is formed in an outer circumferential surface of thecolumnar portion 243, and the male screw 243 a is tightened into afemale screw 251 a formed in the support member 250. Through-holes 243 band 243 c are formed to pass in the vertical direction through theinward portion 242 and the columnar portion 243, and a first adjustingbolt 312 and a second adjusting bolt 322 to be described later areinserted into the through-hole 243 b and the through-hole 243 c,respectively.

When the male screw 241 a formed in the outer circumferential surface ofthe cylindrical portion 241 is tightened into the female screw 210 aformed in the inner circumferential surface of the outer tube 210, thecap 240 is mounted on the outer tube 210. The seal member 245 is fittedto the seal groove 241 b formed in the cylindrical portion 241 to sealthe outer tube 210.

Configuration of Support Member 250

As illustrated in FIG. 3, the support member 250 has the firstcylindrical portion 251 that has a thin-wall cylindrical shape; and asecond cylindrical portion 252 that is formed into a cylindrical shapebelow the first cylindrical portion 251 and has a wall thicker than thewall of the first cylindrical portion 251. The female screw 251 a isformed in an inner circumferential surface of the first cylindricalportion 251, and the male screw 243 a formed in the cap 240 is tightenedinto the female screw 251 a. A ring groove 251 b to which the stopperring 257 is fitted is formed in an outer circumferential surface of thefirst cylindrical portion 251. In addition, the female screw 252 a isformed in an inner circumferential surface of the second cylindricalportion 252, and the male screw 235 a formed in the piston rod 235 istightened into the female screw 252 a.

When the female screw 251 a of the first cylindrical portion 251 istightened onto the male screw 243 a of the cap 240, the support member250 is retained by the cap 240. When the male screw 235 a formed in thepiston rod 235 is tightened into the female screw 252 a of the secondcylindrical portion 252, the piston rod 235 is retained by the secondcylindrical portion 252. Furthermore, when a lock nut 254 is tightenedtoward the support member 250, the piston rod 235 is fixed to not onlythe support member 250 but also the cap 240.

When the male screw 243 a of the cap 240 is tightened into the femalescrew 251 a of the first cylindrical portion 251 of the support member250, the male screw 243 a is tightened into the female screw 251 a untilan upper end surface of the first cylindrical portion 251 abuts againsta lower end surface of the inward portion 242 of the cap 240.Accordingly, the lower end surface of the inward portion 242 of the cap240 functions as an abutting surface against which an upper end surfaceof the support member 250 abuts.

Configuration of Stopper Rubber 255 and the Like

As illustrated in FIG. 3, the stopper rubber 255 is a cylindrical memberthat is molded of an elastic member such as rubber. The stopper rubber255 is arranged in an annular concave portion that is formed by an innercircumference of the cylindrical portion 241 of the cap 240 and an outercircumference of the first cylindrical portion 251 of the support member250.

The stopper plate 256 is a disc-shaped member that has a hole in acenter portion thereof, and the first cylindrical portion 251 of thesupport member 250 passes through the hole.

The stopper ring 257 is a C-shaped retaining ring and is fitted to thering groove 251 b formed in the first cylindrical portion 251 of thesupport member 250. The stopper ring 257 prevents the stopper rubber 255and the stopper plate 256 from falling off.

When the front fork 21 is compressed, an upper end portion of the axleside unit 100 abuts against the stopper plate 256 and the stopper plate256 abuts against the lower end surface of the cylindrical portion 241of the cap 240, and thus upward movement of the axle side unit 100 islimited. At this time, since the stopper rubber 255 is elasticallydeformed, an impact is mitigated at the time the stopper plate 256 abutsagainst the lower end surface of the cylindrical portion 241 of the cap240.

Configuration of Damping Force Generating Apparatus 260

As illustrated in FIG. 4, the damping force generating apparatus 260includes the aforementioned piston 220; a first valve 261 that isarranged below the piston 220 to block a lower end portion of the firstoil path 220 b formed in the piston 220; a second valve 262 that isarranged above the piston 220 to block an upper end portion of thesecond oil path 220 c formed in the piston 220; a first washer 263 thatis arranged below the first valve 261; and a second washer 264 that isarranged above the second valve 262.

As illustrated in FIG. 4, when a lock nut 265 is tightened onto the malescrew 233 a formed in the third cylindrical portion 233 of the pistonbolt 230, the piston 220, the first valve 261, the second valve 262, thefirst washer 263 and the second washer 264 together with the springsupport member 410 and the like are mounted while being interposedbetween the lock nut 265 and a lower end surface of the secondcylindrical portion 232 of the piston bolt 230.

Configuration of Damping Force Adjusting Apparatus 270

The damping force adjusting apparatus 270 includes a first adjustmentmechanism 280 that adjusts a flow rate of oil which circulates betweenthe piston rod side oil chamber 51 and the piston side oil chamber 52through the bypass 60 formed in the piston bolt 230; a second adjustmentmechanism 290 that adjusts a damping force due to bending deformation ofthe second valve 262; and an operation portion 300 that operatesadjustment of the first adjustment mechanism 280 and the secondadjustment mechanism 290.

As illustrated in FIG. 4, the first adjustment mechanism 280 includes aneedle valve 281 that adjusts the circulation area of the bypass 60; afirst push rod 282 that exerts a downward force on the needle valve 281;a coil spring 283 that exerts an upward force on the needle valve 281;and a spring seat 284 that supports a lower end portion of the coilspring 283.

The needle valve 281 is a columnar member which has a flange portion 281a in an upper end portion thereof and of which a lower end portion issharply pointed, and the needle valve 281 is inserted inside the pistonrod 235. The first push rod 282 is a cylindrical or columnar member thatis arranged inside a second push rod 295 to be described later. The coilspring 283 is arranged in the vertical direction between a lower endsurface of the flange portion 281 a of the needle valve 281 and thespring seat 284, and the coil spring 283 is mounted in a radialdirection between an inner circumferential surface of the piston rod 235and an outer circumferential surface of the needle valve 281. The springseat 284 is a disc-shaped member that has a hole in a center portionthereof, and the needle valve 281 passes through the hole. The springseat 284 seals a gap between an inner circumferential surface of thepiston bolt 230 and the outer circumferential surface of the needlevalve 281.

The second adjustment mechanism 290 includes a valve opening suppressionmember 291 that is arranged above the second valve 262 to suppress theopening of the second valve 262; a coil spring 292 that is arrangedabove the valve opening suppression member 291 to exert a downward forceon the valve opening suppression member 291; and a spring receiver 293that is arranged above the coil spring 292 to interpose the coil spring292 between the valve opening suppression member 291 and the springreceiver 293. In addition, the second adjustment mechanism 290 includesa push member 294 that exerts a downward force on the spring receiver293; and the second push rod 295 that exerts a downward force on thepush member 294.

The valve opening suppression member 291 has a first cylindrical portion291 a that is provided in an upper portion and has a cylindrical shape;a second cylindrical portion 291 b that is provided in a lower portion,has inner and outer diameters larger than those of the first cylindricalportion 291 a and has a cylindrical shape; and an intermediate portion291 c that connects the first cylindrical portion 291 a and the secondcylindrical portion 291 b to each other. The first cylindrical portion291 a is fitted around the first cylindrical portion 231 of the pistonbolt 230. A lower end surface of the second cylindrical portion 291 b isin contact with an upper end surface of the second valve 262. A seatsurface on which the coil spring 292 is seated is formed in an upperportion of the intermediate portion 291 c. The intermediate portion 291c is provided intermittently in a circumferential direction in order forthe outside of the valve opening suppression member 291 to communicatewith the bypass 60, and the intermediate portion 291 c allows oil tocirculate between the piston rod side oil chamber 51 and the piston sideoil chamber 52 through the bypass 60.

The spring receiver 293 is a bowl-shaped member that has a hole in acenter portion thereof, and the piston rod 235 passes through the hole.A flange provided in an upper end portion of the spring receiver 293supports an upper end portion of the coil spring 292 and contains thepush member 294 thereinside.

The push member 294 is a plate-like member that has a hole in a centerportion thereof. The hole is larger than an outer diameter of the firstpush rod 282 and smaller than an outer diameter of the second push rod295. The length of the push member 294 is larger than an outer diameterof the piston rod 235. The push member 294 is arranged to move in thevertical direction through the two through-holes 235 c formed in thepiston rod 235.

The second push rod 295 is a cylindrical member of which an innerdiameter is larger than the outer diameter of the first push rod 282 andof which the outer diameter is smaller than an inner diameter of thepiston rod 235. The second push rod 295 is arranged between an outercircumferential surface of the first push rod 282 and the innercircumferential surface of the piston rod 235. A lower end portion ofthe second push rod 295 is in contact with an upper end surface of thepush member 294.

As illustrated in FIG. 3, the operation portion 300 includes a firstoperation portion 310 that moves the first push rod 282 in the verticaldirection; and a second operation portion 320 that moves the second pushrod 295 in the vertical direction. The first operation portion 310 andthe second operation portion 320 are contained in a space that is formedby the cap 240 and the support member 250.

FIG. 6 is a view illustrating a schematic configuration of the firstoperation portion 310 and the second operation portion 320.

The first operation portion 310 includes a first adjusting nut 311 thatexerts a downward force on the first push rod 282; the first adjustingbolt 312 that is screwed into a female screw 311 a formed in the firstadjusting nut 311 to move the first adjusting nut 311 in the verticaldirection; and an oil seal 313 that seals a gap between the firstadjusting bolt 312 and the cap 240.

The second operation portion 320 includes a second adjusting nut 321that exerts a downward force on the second push rod 295; the secondadjusting bolt 322 that is screwed into a female screw 321 a formed inthe second adjusting nut 321 to move the second adjusting nut 321 in thevertical direction; and an oil seal 323 that seals a gap between thesecond adjusting bolt 322 and the cap 240.

The first adjusting nut 311 is a disc-shaped member of which the outerdiameter is slightly smaller than an inner diameter of the firstcylindrical portion 251 of the support member 250. The first adjustingnut 311 has the female screw 311 a into which the first adjusting bolt312 is screwed; and a through-hole 311 b through which a third columnarportion 322 c to be described later of the second adjusting bolt 322passes. A lower end surface of the first adjusting nut 311 is in contactwith an upper end surface of the first push rod 282 to exert a downwardforce on the first push rod 282.

The first adjusting bolt 312 is a member in which a plurality ofcolumnar portions having outer diameters different from each other lineup in the vertical direction. More specifically, the first adjustingbolt 312 has a first columnar portion 312 a that is provided in an upperend portion thereof; a second columnar portion 312 b that is providedbelow the first columnar portion 312 a and has an outer diameter largerthan that of the first columnar portion 312 a; a third columnar portion312 c that is provided below the second columnar portion 312 b and hasan outer diameter smaller than that of the second columnar portion 312b; and a fourth columnar portion 312 d that is provided below the thirdcolumnar portion 312 c and has an outer diameter smaller than that ofthe third columnar portion 312 c.

A groove 312 e (refer to FIG. 3) is formed over the entire circumferenceof an outer circumferential surface of the first columnar portion 312 a,and the groove 312 e is concave inward from the outer circumferentialsurface and the oil seal 313 is fitted to the groove 312 e. In addition,a concave portion 312 f is formed in an upper end surface of the firstcolumnar portion 312 a and is concave downward from the upper endsurface.

The outer diameter of the second columnar portion 312 b is larger thanan inner diameter of the through-hole 243 b formed in the cap 240.

A male screw 312 g is formed in an outer circumferential surface of thethird columnar portion 312 c, and the male screw 312 g is screwed intothe female screw 311 a formed in the first adjusting nut 311.

The second adjusting nut 321 is a disc-shaped member of which an outerdiameter is slightly smaller than the inner diameter of the firstcylindrical portion 251 of the support member 250. The second adjustingnut 321 has the female screw 321 a into which the second adjusting bolt322 is screwed; and a through-hole 321 b through which the fourthcolumnar portion 312 d of the first adjusting bolt 312 passes. Inaddition, a through-hole 321 c is formed in a center portion of thesecond adjusting nut 321, and the first push rod 282 passes through thethrough-hole 321 c. A lower end surface of the second adjusting nut 321is in contact with an upper end surface of the second push rod 295 toexert a downward force on the second push rod 295.

The second adjusting bolt 322 is a member in which a plurality ofcolumnar portions having outer diameters different from each other lineup in the vertical direction. More specifically, the second adjustingbolt 322 has a first columnar portion 322 a that is provided in an upperend portion thereof; a second columnar portion 322 b that is providedbelow the first columnar portion 322 a and has an outer diameter largerthan that of the first columnar portion 322 a; a third columnar portion322 c that is provided below the second columnar portion 322 b and hasan outer diameter smaller than that of the second columnar portion 322b; and a fourth columnar portion 322 d that is provided below the thirdcolumnar portion 322 c and has an outer diameter smaller than that ofthe third columnar portion 322 c.

A groove 322 e (refer to FIG. 3) is formed over the entire circumferenceof an outer circumferential surface of the first columnar portion 322 a,and the groove 322 e is concave inward from the outer circumferentialsurface and the oil seal 323 is fitted to the groove 322 e. In addition,a concave portion 322 f is formed in an upper end surface of the firstcolumnar portion 322 a and is concave downward from the upper endsurface.

The outer diameter of the second columnar portion 322 b is larger thanan inner diameter of the through-hole 243 c of the columnar portion 243formed in the cap 240.

The outer diameter of the third columnar portion 322 c is smaller thanan inner diameter of the through-hole 311 b formed in the firstadjusting nut 311.

A male screw 322 g is formed in an outer circumferential surface of thefourth columnar portion 322 d, and the male screw 322 g is screwed intothe female screw 321 a formed in the second adjusting nut 321.

The operation portion 300 having the aforementioned configuration iscontained in the space that is formed by the cap 240 and the supportmember 250. At this time, the first columnar portion 312 a of the firstadjusting bolt 312 is inserted into the through-hole 243 b, and thefirst columnar portion 322 a of the second adjusting bolt 322 isinserted into the through-hole 243 c. In addition, the upper end surfaceof the first push rod 282 abuts against the lower end surface of thefirst adjusting nut 311, and the upper end surface of the second pushrod 295 abuts against the lower end surface of the second adjusting nut321.

Since the third columnar portion 322 c of the second adjusting bolt 322is fitted into the through-hole 311 b of the first adjusting nut 311,the first adjusting nut 311 into which the first adjusting bolt 312 isscrewed is prevented from being rotated and is moved in the verticaldirection by rotation operation of the first adjusting bolt 312.Accordingly, the first push rod 282 moves in the vertical direction.

In contrast, since the fourth columnar portion 312 d of the firstadjusting bolt 312 is fitted into the through-hole 321 b of the secondadjusting nut 321, the second adjusting nut 321 into which the secondadjusting bolt 322 is screwed is prevented from being rotated and ismoved in the vertical direction by rotation operation of the secondadjusting bolt 322. Accordingly, the second push rod 295 moves in thevertical direction.

Operation of Front Fork 21

Hereinafter, operation of the front fork 21 having the aforementionedconfiguration according to the embodiment will be described.

Extension Stroke

FIGS. 7A and 7B are views illustrating operation of an extension stroke.FIG. 7B is a view illustrating a state where the front fork 21 isextended from a state in FIG. 7A.

As illustrated in FIGS. 7A and 7B, when the inner tube 110 retreats fromthe outer tube 210, a distance between the oil ring 135 fitted to thering groove 133 a of the rod guide case 130 and the guide bush 211fitted into the outer tube 210 becomes short, and a volume of theannular oil chamber 20 becomes small. Accordingly, oil in the annularoil chamber 20 flows into the working oil chamber 50 through thecommunication hole 114 of the inner tube 110 (refer to an arrow 71). Inaddition, since, by movement of the piston 220, a volume of the pistonrod side oil chamber 51 of the working oil chamber 50 is decreased and avolume of the piston side oil chamber 52 is increased, the oil flowinginto the working oil chamber 50 from the annular oil chamber 20 flowsinto the piston side oil chamber 52 from the piston rod side oil chamber51 through the bypass 60 or the first oil path 220 b formed in thepiston 220. At this time, since the cross-sectional area of the annularoil chamber 20 is set to be larger than the cross-sectional area of thepiston rod 235, a volume decrease V1 of the annular oil chamber 20resulting from extension operation of the front fork 21 is larger than avolume decrease V2 resulting from retreat of the piston rod 235 from theworking oil chamber 50, and since the communication path 40 is a paththat is formed in the rod guide case 130 in order for the annular oilchamber 20 to communicate with the annular gap 25, surplus oil (V1−V2)in the working oil chamber 50 flows through the communication path 40from the annular oil chamber 20 into the annular gap 25 formed betweenthe rod guide case 130 and the inner tube 110 (refer to an arrow 72).Since the communication hole 131 c is formed in the lower end portion ofthe cylindrical portion 131 of the rod guide case 130, oil flows intothe oil chamber 46 of the oil reservoir chamber 45 from the annular gap25 (refer to an arrow 73).

In addition, since, by movement of the piston 220, the volume of thepiston rod side oil chamber 51 of the working oil chamber 50 isdecreased and the volume of the piston side oil chamber 52 is increased,the oil flowing into the working oil chamber 50 from the annular oilchamber 20 flows into the piston side oil chamber 52 from the piston rodside oil chamber 51 through the bypass 60 or the first oil path 220 bformed in the piston 220. In contrast, when pressure inside the pistonrod side oil chamber 51 is increased by decrease in the volume of thepiston rod side oil chamber 51, the upper end surface of the flange 151a of the check valve 151 abuts against the upper end surface of thesecond concave portion 142 of the rod guide case 130, and flow of oilfrom the working oil chamber 50 into the oil reservoir chamber 45 issuppressed. In addition, the oil seal 145 is fitted to the seal groove132 b formed in the inward portion 132 of the rod guide case 130, andthe oil seal 145 prevents oil from flowing into the annular gap 25 fromthe working oil chamber 50.

During the extension stroke, a damping force is generated due to pathresistance in the communication path 40 of the rod guide case 130 whenoil flows into the annular gap 25 from the annular oil chamber 20. Inaddition, in a low speed region, a damping force is generated due topath resistance in the bypass 60 of which a circulation area is adjustedby adjusting a degree of opening of the needle valve 281 of the firstadjustment mechanism 280. In a medium to high speed region, a dampingforce is generated due to bending deformation of the first valve 261that blocks the first oil path 220 b formed in the piston 220 of thedamping force generating apparatus 260.

Compression Stroke

FIGS. 8A and 8B are views illustrating operation of a compressionstroke. FIG. 8B is a view illustrating a state where the front fork 21is compressed from a state in FIG. 8A.

As illustrated in FIGS. 8A and 8B, when the inner tube 110 enters theouter tube 210, a distance between the oil ring 135 fitted to the ringgroove 133 a of the rod guide case 130 and the guide bush 211 fittedinto the outer tube 210 becomes large, and the volume of the annular oilchamber 20 becomes large. Accordingly, oil in the working oil chamber 50flows into the annular oil chamber 20 through the communication hole 114of the inner tube 110 (refer to an arrow 81). In addition, since, bymovement of the piston 220, the volume of the piston side oil chamber 52of the working oil chamber 50 is decreased and the volume of the pistonrod side oil chamber 51 is increased, oil flows into the piston rod sideoil chamber 51 from the piston side oil chamber 52 through the bypass 60or the second oil path 220 c formed in the piston 220. At this time,since the cross-sectional area of the annular oil chamber 20 is set tobe larger than the cross-sectional area of the piston rod 235, a volumeincrease V3 of the annular oil chamber 20 resulting from compressionoperation of the front fork 21 is larger than a volume increase V4resulting from entry of the piston rod 235 into the working oil chamber50, and a deficient amount (=V3−V4) compared to the necessary supplyamount of oil to the annular oil chamber 20 (=V3) is supplied to theannular oil chamber 20 from the oil reservoir chamber 45 through thecheck valve 151 (refer to an arrow 82). In addition, a deficient amountcompared to the necessary supply amount of oil to the annular oilchamber 20 is supplied to the annular oil chamber 20 from the oilreservoir chamber 45 through the communication hole 131 c, the annulargap 25 and the communication path 40 (refer to an arrow 83). However,the oil seal 145 is fitted to the seal groove 132 b formed in the inwardportion 132 of the rod guide case 130, and thereby preventing oil fromflowing into the working oil chamber 50 from the annular gap 25.

During the compression stroke, a damping force is generated due to pathresistance in the communication path 40 of the rod guide case 130 whenoil flows into the annular oil chamber 20 from the annular gap 25. Inaddition, in the low speed region, a damping force is generated due topath resistance in the bypass 60 of which the circulation area isadjusted by adjusting the degree of opening of the needle valve 281 ofthe first adjustment mechanism 280. In the medium to high speed region,a damping force is generated due to bending deformation of the secondvalve 262 that blocks the second oil path 220 c formed in the piston 220of the damping force generating apparatus 260. The damping forceresulting from the bending deformation of the second valve 262 isadjusted by the second adjustment mechanism 290.

As described above, in the front fork 21 according to the embodiment,during the extension operation, oil flows into the annular gap 25 fromthe annular oil chamber 20 through the communication path 40 and reachesthe oil chamber 46 in the oil reservoir chamber 45 through thecommunication hole 131 c. Accordingly, for example, even though air istrapped in an upper portion of the annular oil chamber 20, the air isdischarged into the oil chamber 46 of the oil reservoir chamber 45 by apressurized oil that flows into the annular gap 25 from the annular oilchamber 20 through the communication path 40, and the discharged airreaches the air chamber 47. In contrast, during the compression stroke,pressure in the annular oil chamber 20 becomes negative compared to theair chamber 47. However, the communication hole 131 c formed in the rodguide case 130 is present in the lower end portion of the cylindricalportion 131 and inside the oil chamber 46 of the oil reservoir chamber45, oil in the oil reservoir chamber 45 flows into the annular oilchamber 20 through the annular gap 25 and the communication path 40. Forthis reason, air in the oil reservoir chamber 45 is not sucked into theannular oil chamber 20.

In the front fork 21 according to the embodiment, it is possible tosuppress occurrence of air bubble entrapment in the upper portion of theannular oil chamber 20 or an upper portion of the annular gap 25.Accordingly, it is possible to suppress occurrence of an impulse soundcaused by occurrence of the air bubble entrapment in the upper portionof the annular oil chamber 20 or in the upper portion of the annular gap25.

Configuration of Discharging Air Trapped in Operation Portion 300

Subsequently, a configuration of discharging air trapped in theoperation portion 300 will be described.

FIG. 9A is a view illustrating cross-sections of the cap 240, thesupport member 250, the stopper rubber 255 and the outer tube 210. FIG.9B is a cross-sectional view of portion IX-IX in FIG. 9A. Thethrough-hole 243 b and the through-hole 243 c are formed at twocircumferential locations in the inward portion 242 and the columnarportion 243 of the cap 240, the first adjusting bolt 312 is insertedinto the through-hole 243 b and the second adjusting bolt 322 isinserted into the through-hole 243 c. The cross-sectional viewillustrated in FIG. 9A is a cross-sectional view of a portion in whichthe through-holes 243 b and 243 c are not formed.

A columnar portion side concave portion 243 d that is concave inward isformed as a partial circumferential area in the outer circumferentialsurface of the columnar portion 243 of the cap 240. In addition, aninward portion side concave portion 242 a that is concave upward fromthe lower end surface is formed as a partial circumferential area in theinward portion 242 of the cap 240 at a position corresponding to aposition of the columnar portion side concave portion 243 d. In otherwords, as illustrated in FIG. 9A, the columnar portion side concaveportion 243 d and the inward portion side concave portion 242 a as anexample of the upward concave portion are continuously formed, and thecolumnar portion side concave portion 243 d and the inward portion sideconcave portion 242 a function as the communication path 41 throughwhich a space 53, as an example of the upper portion space, inside thefirst cylindrical portion 251 of the support member 250 communicateswith the air chamber 47.

As illustrated in FIG. 9A, a check valve 246 is provided as an exampleof a non-return valve between the lower end surface of the inwardportion 242 of the cap 240 and the upper end surface of the firstcylindrical portion 251 of the support member 250, and the check valve246 is made of a thin plate to cover an opening portion of the inwardportion side concave portion 242 a. As illustrated in FIG. 9B, when thecheck valve 246 is seen from above, the check valve 246 has a sizelarger than that of the inward portion side concave portion 242 a, andwhen pressure in the air chamber 47 is higher than pressure in the firstcylindrical portion 251 of the support member 250, the check valve 246abuts against the lower end surface of the inward portion 242 and blocksan opening portion of the communication path 41. In contrast, whenpressure in the first cylindrical portion 251 of the support member 250is higher than pressure in the air chamber 47, the check valve 246 iselastically deformed to open the opening portion of the communicationpath 41 and to discharge air in the space 53 inside the firstcylindrical portion 251 of the support member 250 into the air chamber47. The check valve 246 may be a donut-shaped plate that is provided inan outer circumference of the columnar portion 243 of the cap 240.

Accordingly, during extension operation of the front fork 21, pressurein the piston rod side oil chamber 51 is increased by upward movement ofthe piston 220 and decrease in the volume of the annular oil chamber 20,and the increased pressure is transmitted to the space 53 inside thefirst cylindrical portion 251 of the support member 250 in which theoperation portion 300 is arranged via the through-hole 235 c of thepiston rod 235, an inner portion of the piston rod 235 (inner space ofthe piston rod), thereby discharging air in the space 53 into the airchamber 47 through the communication path 41 (refer to an arrow 74 inFIG. 7B). In contrast, during compression operation of the front fork21, even though pressure in the air chamber 47 increases, air in the airchamber 47 is not sucked into the space 53 inside the first cylindricalportion 251 of the support member 250 in which the operation portion 300is arranged since the check valve 246 blocks the opening portion of thecommunication path 41.

Accordingly, in the front fork 21 according to the embodiment, it ispossible to suppress occurrence of the air bubble entrapment in thespace 53 in which air is present and in which pressure increases duringthe extension operation inside the first cylindrical portion 251 of thesupport member 250. Accordingly, it is possible to suppress occurrenceof the impulse sound caused by occurrence of the air bubble entrapmentin the space 53 inside the first cylindrical portion 251 of the supportmember 250.

Another Embodiment of Configuration of Discharging Air Trapped inOperation Portion 300

FIG. 10 is a view illustrating cross-sections of the cap 240, thesupport member 250, the stopper rubber 255 and the outer tube 210according to another embodiment.

In another embodiment, a configuration of communicating the space 53inside the first cylindrical portion 251 of the support member 250 withthe air chamber 47 is different from aforementioned embodiment. That is,as illustrated in FIG. 10, a through-hole 251 c is formed in a portionof the first cylindrical portion 251 of the support member 250 which isbelow the columnar portion 243 of the cap 240, and the through-hole 251c passes through the first cylindrical portion 251 in a directionorthogonal to the vertical direction (in a radial direction). Thethrough-hole 251 c functions as a communication path 42 through whichthe space 53 inside the first cylindrical portion 251 of the supportmember 250 communicates with the air chamber 47.

Even in another embodiment, during extension operation of the front fork21, pressure in the piston rod side oil chamber 51 is increased byupward movement of the piston 220 and decrease in the volume of theannular oil chamber 20, and the increased pressure is transmitted to thespace 53 inside the first cylindrical portion 251 of the support member250 in which the operation portion 300 is arranged into the air chamber47 through the through-hole 235 c of the piston rod 235, the innerportion of the piston rod 235, thereby discharging air in the space 53into the air chamber 47 through the communication path 42. At this time,the stopper rubber 255 that is provided around the first cylindricalportion 251 of the support member 250 is elastically deformed or ismoved downward to open an opening portion of the communication path 42.In contrast, during compression operation of the front fork 21, eventhough pressure in the air chamber 47 increases, air in the air chamber47 is not sucked into the space 53 inside the first cylindrical portion251 of the support member 250 in which the operation portion 300 isarranged since the stopper rubber 255 blocks the opening portion of thecommunication path 42. Accordingly, even in another embodiment, duringthe extension operation, it is possible to suppress occurrence of theair bubble entrapment in the space 53 in which air is present and inwhich pressure increases during the extension stroke inside the firstcylindrical portion 251 of the support member 250. Accordingly, it ispossible to suppress occurrence of the impulse sound caused byoccurrence of the air bubble entrapment in the space 53 inside the firstcylindrical portion 251 of the support member 250.

In another embodiment, the communication path 42 is formed in thethrough-hole 251 c formed in the first cylindrical portion 251 of thesupport member 250, and the space 53 inside the first cylindricalportion 251 of the support member 250 communicates with the air chamber47 through the communication path 42. However, the invention is notlimited to another embodiment. A communication path may be configured bythe columnar portion side concave portion 243 d of the cap 240 that isshown in FIGS. 9A and 9B, and a through-hole that is formed in a portionof the first cylindrical portion 251 of the support member 250 whichfaces the columnar portion side concave portion 243 d of the cap 240 andthat passes through the first cylindrical portion 251 in the directionorthogonal to the vertical direction (in the radial direction), and thespace 53 inside the first cylindrical portion 251 of the support member250 communicates with the air chamber 47 through the communication path.Instead of the communication path being configured by two members thatare the cap 240 and the support member 250, when the communication pathis formed in only one of the cap 240 and the support member 250,productivity can be improved since the cap 240 can be assembled into thesupport member 250 without regard to relative positions of configurationportions of the communication path during the assembly of the cap 240and the support member 250.

What is claimed is:
 1. A suspension apparatus comprising: a cylindricalouter tube; an inner tube which is coaxially arranged inside the outertube to move in an axial direction relative to the outer tube; a pistoninserted into the inner tube; a piston rod of which one end portionretains the piston and which moves together with the outer tube withrespect to the inner tube; a partition wall member that is mounted to anupper end portion of the inner tube to define an upper end portion of anannular oil chamber which is formed between an inner circumferentialsurface of the outer tube and an outer circumferential surface of theinner tube, that has a bowl portion formed into a bowl shape locatedinside the inner tube, and that divides a space inside the inner tubeinto an upper space which is a space above the bowl portion and a lowerspace which is a space below the bowl portion; a cap that covers anupper opening portion of the outer tube; and a support member of whichone end portion is retained by the cap, and of which the other endportion supports the other end portion of the piston rod, wherein athrough-hole is formed in a portion of the inner tube which is below thepartition wall member to communicate the annular oil chamber with thelower space, an inner space of the piton rod is a space inside thepiston rod and communicates with the lower space, the support member isa cylindrical member and forms an upper portion space between the capand the support member, and the upper portion space communicates withthe inner space of the piston rod, and at least one of the cap and thesupport member is provided with a communication path through which theupper portion space communicates with the upper space.
 2. The suspensionapparatus according to claim 1, wherein the cap has an abutting surfaceagainst which an upper end surface of the support member abuts, thecommunication path has an upward concave portion that is concave upwardfrom the abutting surface of the cap, and the suspension apparatusfurther comprises a non-return valve that is arranged between theabutting surface of the cap and the upper end surface of the supportmember, that allows flow of air from the upper portion space to theupper space through the communication path, and that suppresses flow ofair from the upper space to the upper portion space.
 3. The suspensionapparatus according to claim 1, wherein the communication path is acommunication hole which is formed in a portion of the support memberwhich is below the cap and through which the upper portion spacecommunicates with the upper space, and rubber is arranged around thesupport member in the upper space.
 4. The suspension apparatus accordingto claim 1, wherein the piston retains a dividing member that dividesthe lower space into an upper positioning space which is a spacepositioned above the dividing member and a lower positioning space whichis a space positioned below the dividing member, and has a spacecommunication hole that is a hole to communicate the upper positioningspace with the lower positioning space, the suspension apparatus furthercomprises an adjustment mechanism that adjusts the rate of a fluidpassing through the space communication hole of the piston, and anoperation portion operating the adjustment mechanism is arranged insidethe upper portion space.
 5. The suspension apparatus according to claim2, wherein the piston retains a dividing member that divides the lowerspace into an upper positioning space which is a space positioned abovethe dividing member and a lower positioning space which is a spacepositioned below the dividing member, and has a space communication holethat is a hole to communicate the upper positioning space with the lowerpositioning space, the suspension apparatus further comprises anadjustment mechanism that adjusts the rate of a fluid passing throughthe space communication hole of the piston, and an operation portionoperating the adjustment mechanism is arranged inside the upper portionspace.
 6. The suspension apparatus according to claim 3, wherein thepiston retains a dividing member that divides the lower space into anupper positioning space which is a space positioned above the dividingmember and a lower positioning space which is a space positioned belowthe dividing member, and has a space communication hole that is a holeto communicate the upper positioning space with the lower positioningspace, the suspension apparatus further comprises an adjustmentmechanism that adjusts the rate of a fluid passing through the spacecommunication hole of the piston, and an operation portion operating theadjustment mechanism is arranged inside the upper portion space.